Deuterostome clade


  • Phylum Echinoderms (Invertebrates)
  • Phylum Chordata (mostly Vertebrates)


  • Deuterostome = Developmental similarities
    • radial cleavage of embryo
    • anus forms first (then mouth)


  • HOWEVER: other animal phyla share some of these traits
    • Deuterostomes now mostly defined by molecular evidence

Protostome vs Deuterostome

Groups differ in how the digestive system developes



  • Two groups differ by embryonic development of the blastopore (the first developmental opening) and the alignment of embryonic cells after fertilization


  • Protostome = Mouth develops first


  • Deuterostome = Mouth develops second

Sexual reproduction in animals results in diploid zygote

Radial Cleavage: daughter cells are exactly on top of one another

Phylum Echinoderms


  • Translates to ‘Spiny Skin’
    • sea stars and urchins
    • slow moving and marine
    • adult = radial, larval = bilateral


  • Thin epidermis covered in hard plates
    • often with bumps or spines

Phylum Echinoderms


  • Translates to ‘Spiny Skin’
    • sea stars and urchins
    • slow moving and marine
    • adult = radial, larval = bilateral


  • Thin epidermis covered in hard plates
    • often with bumps or spines


  • Possess a unique water vascular system
    • flexible hydraulic canals = tube feet

Phylum Chordata (mostly vertebrates)


  • All chordates share 4 traits
  • Some only in embryo stages
  1. Notochord
  2. Dorsal, hollow nerve cord
  3. Pharyngeal slits
  4. Muscular, Post-anal tail


  • 2 invertebrates groups that are more related to vertebrates
    • Cephlachordata (lancelets)
    • Urochordates (tunicates)

Lancelets and Tunicates (invertebrates)

Vertebrates are chordates with a backbone




  • Possess skeletal and nervous systems
    • simple to complex backbones
    • lots of unique genes (eg. HOX)



  • Derived trait = neural crest
    • special stem cells near neural tube in embryo
    • give rise to many vertebrate traits
    • e.g.. teeth, skull, cartilage, etc

History of backbones: ~525 million years old


  • Evolved while predators where developing
    • Cambrian period
    • Ocean origins


  • Vertebrate: series of bones that make up the vertebral column
    • 57,000 species


  • Vertebrates with limbs colonized land 365 mya
  1. Amphibians
  2. Reptiles (w/ birds)
  3. Mammals

Hagfish and Lampreys


  • Only members of vertebrates without jaws
    • sister group of jawless fish


  • Have rudimentary backbones
    • more cartilage than bone


  • Hagfish escape by releasing slime
    • slime threads act as hydrogel and rapidly expand when mixed with water
    • researched to stop bleeding in surgery

Hagfish and Lampreys


  • Only members of vertebrates without jaws
    • sister group of jawless fish


  • Have rudimentary backbones
    • more cartilage than bone


  • Many Lamprey are parasitic on fish
    • invaded Great Lakes
    • native to Chesapeake Bay

Vertebrates with jaws

Sharks and rays


  • ‘Cartilage fishes’: skeletons mostly cartilage
    • often with calcium
    • originated 400 mya


  • Streamlined body for swift swimming
    • poor maneuverability
    • stay in near constant motion


  • Birth via eggs or young develop inside mother


  • Modern species diversity massively reduced

Ray-finned fish


  • Phylogeny: large new vertebrate group with bony endoskeletion
    • fishes = aquatic groups


  • Add lungs/lung derivatives to phylogeny


  • Important derived traits for fishes:
    • operculum:
    • swim bladder:


  • Ray-finned: bony rays that support fins
    • trout, sea horses, eels


Evolution had to solve a density problem for bony fishes



  • A fish has a density of about 1.076
    • freshwater has a density of 1.0
    • saltwater has a density of 1.026


  • Bone is nearly twice as dense as cartilage


  • Swimming is energy expensive
    • resting on the bottom may not be practical


  • Evolution of the swim bladder set fish free

Lobe-finned fish and Lungfish

  • Lobe-finned: rod-shaped bone surrounded by muscle in fins
    • two living species, both Coelacanths
    • ancestors to earliest tetrapods


  • Lungfish are freshwater vertebrates
    • have the ability to breath air
    • can live out of water in a state of hibernation for up to a year

Evolution of Tetrapod group




  • Lobe fins gradually evolved into limbs
    • Tetrapods colonized land 365 mya
    • move away from fish-like vertebrates



  • Tetrapod derived trait = limbs with digits
    • supports weight
    • digits efficiently support movement

Tiktaalik fossil (aka ‘Fishapod’)





  • Fossils found in river beds


  • Selection of many terrestrial traits
    • head separated from body by a neck
    • more vertebrate to allow head to swing
    • bones of pelvis fuse to backbone
    • many species lost gills (became ears)

Amphibians (frogs and salamanders)


  • Include salamanders, frogs and caecilians

    • 6,000 species

    • caecilians lost legs


  • Rely on skin for gas exchange
    • live in moist habitats


  • Name means ‘dual life’
    • some have aquatic tadpole larvae
    • more related to metamorphosis
    • gills → legs, lungs, eardrums

Amniotes: tetrapod with terrestrial egg (also rib cage)

Amniotic egg contains 4 membranes around embryo. Surrounds embryo with amniotic fluid

Reptiles



  • Lizards, snakes, turtles, crocs and BIRDS
    • many extinct groups
    • small (16mm) to large (12m)


  • Scales with keratin


  • Lay shelled eggs on land


  • Most reptiles are ectothermic

Reptiles



  • Lizards, snakes, turtles, crocs and BIRDS
    • many extinct groups
    • small (16mm) to large (12m)


  • Scales with keratin


  • Lay shelled eggs on land


  • Most reptiles are ectothermic

The origin of birds (members of the reptile family tree)

Mammals


  • Large adaptive radiation post dinosaurs
    • predators, herbivores, flying, aquatic
    • Monotremes = platypus (egg laying)
    • Maruspials = pouched mammals
    • Eutherians = placental mammals


  • Derived Trait: Mammary glands
    • produce milk for offspring


  • Derived Trait: Hair
    • insulation/water saver